Although the month and date of Jesus' birth are unknown, by the early-to-mid fourth century the Western Christian Church had placed Christmas on December 25, a date that was later adopted in the East. Today, most Christians celebrate on December 25 in the Gregorian calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world.
However, some Eastern Christian Churches celebrate Christmas on December 25 of the older Julian calendar, which currently corresponds to January 7 in the Gregorian calendar, the day after the Western Christian Church celebrates the Epiphany. This is not a disagreement over the date of Christmas as such, but rather a preference of which calendar should be used to determine the day that is December 25.
In the Council of Tours of 567, the Church, with its desire to be universal, "declared the twelve days between Christmas and Epiphany to be one unified festal cycle", thus giving significance to both the Western and Eastern dates of Christmas